This disorder produces noncancerous tumors of the peripheral nerves called plexiform neurofibromas, explained senior author Dr. Brigitte Widemann, chief of pediatric oncology for the U.S. National Cancer Institute's Center for Cancer Research.

These tumors can occur anywhere in the body, and they can grow so large that they can cause pain, disability and disfigurement, Widemann said.

"You might see a baby and you think the face is completely symmetric," Widemann said. "By one year of age you see one cheek is larger, and by three years it is a very disfiguring tumor that might also affect swallowing, speech or breathing if it's close to the airway."

Plexiform neurofibromas can cause vision loss if they develop in an eye socket, motor weakness if they impinge on the nerves leading to the arms or legs, or bowel and bladder dysfunction if they occur near the digestive system, Widemann said.

Neurofibromatosis type 1 affects about one in every 3,000 people, Widemann said. Among people with NF1, between 20 percent and 50 percent will develop plexiform neurofibromas, most often in early childhood.

Until now, surgery has been the only treatment option. About 75 percent of patients who undergo surgery to remove their tumor are cured, according to Children's National Health System in Washington, D.C.

But many children cannot undergo surgery to remove their tumors, Widemann said.

"These tumors are many times right next to the nerves, they wrap around big blood vessels, they're very big and surgery sometimes is just not an option," she said.

Widemann and her colleagues suspected selumetinib might be useful in treating plexiform neurofibromas. Lab experiments in mice found that the drug interferes with the signaling pathways that influence the growth of the tumors.

The phase 1 clinical trial enrolled 24 children with plexiform neurofibromas. The kids were all given twice-daily doses of the oral drug continuously over treatment cycles that averaged 30 months.

The drug caused tumors to shrink at least 20 percent and as much as 50 percent in 17 of the 24 children, Widemann said.

The most successful case involved a patient who had a large tumor in her hip and buttock that rendered the girl wheelchair-bound and pain-ridden, Widemann said.

"Her tumor shrank by almost 50 percent," Widemann said. "She was able to get off her pain medicine, she was able to walk extended distances, and her disfigurement was much reduced."

Another patient who couldn't lift her arm due to her tumor was able to raise it all the way up following treatment with the drug, Widemann added.

The study began in September 2011, and most of the kids are still taking selumetinib. The most common side effects were acne-like skin rashes and gastrointestinal problems.

"They have been on this for a long time," Widemann said. "The side effects are very manageable."

Phase II trials already have started to confirm the safety and effectiveness of the drug, she said.

The drug appears promising, but needs further study, said Dr. Krzysztof Misiukiewicz, an associate professor of medical oncology with the Icahn School of Medicine at Mount Sinai in New York City.

"It looks like a large portion of the patients had a response, but it took about 20 months on average to get a response," he said. "It is not something that happens immediately with a few doses."

This trial did determine that kids cannot tolerate adult-level doses of selumetinib, said Dr. Susan Chang, co-leader of the Neurologic Oncology Program at UCSF Helen Diller Family Comprehensive Cancer Center in San Francisco.

"This study showed that the maximal tolerated dose in children was 60 percent of that for adults, emphasizing the need to perform phase 1 trials specifically in the pediatric population before expanding to studies that evaluate efficacy," Chang said.

The U.S. National Cancer Institute funded the study. AstraZeneca, the drug's maker, supplied the medicine and performed some blood analysis. The study appears in the Dec. 29 issue of the New England Journal of Medicine.